Changing Time Series from Start to End of Month

[illmattic]

Hello,

I'm pulling monthly data from Quandl and it gives me the follwing:

USA_m1 = quandl.get('FRED/M1NS', authtoken=api_key, start_date='2000-01-01')
            
            Value
Date 
2020-01-01  3981.9
2020-02-01  3946.1
2020-03-01  4299.2
2020-04-01  4869.6
2020-05-01  5043.8

How would I change the index so that it is the end of the month where value 5043.8 would have a date of 2020-04-30 instead of 2020-05-01?
Thank you.